The effects of administering deuterated L-DOPA on the formation and metabolism of peripheral and central non- deuterated catecholamines as described in the 1986 Annual Report is now completed. Our interest had shifted towards comparing central and peripheral metabolism of D-DOPA with that of L-DOPA. We found that both D- and L-DOPA gave rise to DA by about the same efficiency. This unexpected finding led us to characterize these two amino acids biochemically as well as behaviorally. We also carried out additional experiments in order to explore the underlining mechanisms that are responsible for the formation of dopamine from D-DOPA.